(a) Field of the Invention
The present invention relates to a fast block mode determining method for motion estimation, and an apparatus thereof.
(b) Description of the Related Art
Moving picture technology is being utilized in video conferencing, high definition television, video on demand (VOD) receivers, personal computers supporting MPEG (moving picture experts group) images, game tools, terrestrial digital broadcasting receivers, digital satellite broadcasting receivers, cable television, etc. Moving picture data needs to be compressed because its amount of data is greatly increased in digitalizing an analogue signal. A moving picture is formed of a plurality of frames, and similarities exist between neighboring frames or between blocks or pixels in the same frame. This similarity of the image signal enables predictive encoding of the image, so that a highly efficient image signal compression may be performed.
Generally, there are three kinds of image data compression methods. These are i) a temporal redundancy reducing method, ii) a spatial redundancy reducing method, and iii) a statistical characteristic of code utilizing method. A motion estimation and compensation method is a representative example of the temporal redundancy reducing method, and this is adopted and utilized in most moving image compression standards such as MPEG and H.263.
The motion estimation method shows substantial performance in reducing a bit ratio by eliminating temporal redundancy in moving image encoding. The motion estimation method may be largely divided into a pixel-based matching scheme and a block-based matching scheme. Generally, since motion is expressed by a large block unit, the block-based estimation method is broadly used.
According to the block-based estimation method, an image is divided into several blocks having the same size, and a block which is best matched with a current block is searched for in previous image blocks. Here, a motion vector corresponding to a difference between the current block and the searched block is calculated and encoded, so that the motion estimation may be performed. When evaluating a match between the blocks, various matching functions may be utilized, and the generally used scheme is to utilize an SAD (sum of absolute difference) which is a sum of absolute values of differences between pixels of the two blocks.
However, a moving picture encoding device of the H.264 standard uses a cost function based on rate-distortion optimization instead of the conventional scheme based on the SAD. Unlike conventional moving picture encoding schemes based on large 16×16 or 8×8 blocks, the H.264 standard uses 8 different kinds of block modes, and selects a mode having a minimum value among the block modes in order to obtain high compression efficiency and high image quality. In other words, the H.264 standard provides variable-block-based motion estimation of various block sizes. This provides many advantages in encoding efficiency. In addition, according to the H.264 standard, a motion vector prediction based on a quarter-pixel is performed, so that more accurate motion estimation may be enabled and encoding efficiency may be increased. However, compared with other encoding schemes, while encoding efficiency may be increased by using a quarter-pixel search, a minimum of 16 times more motion estimation operations need to be performed. This is the main reason for speed falloff in H.264 video encoding.
Therefore, efforts to reduce the motion estimation time, which is the most time-consuming process in moving picture encoding, are still ongoing.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.